Mineral fiber is a low cost, fibrous mineral product that can be manufactured from a variety of materials including igneous rock and basalt, from slag produced by the blast furnaces used to make steel and other metals, and from waste products from the phosphate industry. Generally speaking, although mineral fiber has an appearance similar to glass fiber, its chemical composition is significantly different from that of glass fiber, due to high calcium and magnesium content in the mineral fiber and a relatively low proportion of silica and alumina in it. Mineral fiber is suitable for use in many high temperature applications, 1200.degree. to 1800.degree. F. Industrial uses are many and varied.
Known processes for the manufacture of mineral fiber material usually start by melting a mineral charge in any one of a variety of different types of furnace, including cupola melters similar to blast furnaces, electrical furnaces, and gas fired furnaces. The molten material from the initial furnace or melter stage is then spun by any of a variety of means to form discrete fibers. The fibers are then collected in a large chamber from which the output is a fiber blanket, a fiber board, or even pellets of loose fiber.
Most known processes convert only approximately fifty percent to seventy-five percent of the molten minerals into usable mineral fiber. The remainder of the original molten mineral ends up as fine, substantially spherical shot waste, which has little or no useful purpose and constitutes a contamination in the finished product. Separation of this fine, substantially spherical shot waste from the mineral fibers has been attempted; typical techniques include centrifugal air separation, air transport dropout devices, and a variety of screening methods that have used gravity driven inclined screens as well as screens with both oscillating and rotary mechanical drives.
These separation or cleaning techniques, however, may also introduce some substantial problems. Thus, the high aspect ratio (diameter in relation to fiber length) of the fibrous material, in combination with the abundant mechanical contact that occurs in any of the known separation techniques, results in the mineral fiber product becoming clumped or entangled (prilled) into relatively tight, small nodules or pellets. These pellets can be quite difficult to disperse into viscous liquids where they might otherwise be used (e.g. in caulks, plastics, etc.). The pellets can also be difficult to handle in dry, powder-like formations.